Interventional procedures of different types in a vascular system, in particular the blood vascular system, of a patient have already been proposed. In such instances, a suitable instrument, a catheter for example, on which further treatment instruments may be arranged where necessary, is guided through the vascular system to the treatment site. Image monitoring may take place so that the positioning of the instrument and the treatment may be monitored. For this purpose X-ray images, in particular fluoroscopic images, are acquired in which the instrument may be clearly identified. That said, however, fluoroscopic images reveal the vascular system less clearly, so it is known in this regard to use a vascular dataset which contains the anatomical information relating to the vascular system and from which it is possible to generate overlay images that may be superimposed on the X-ray image to achieve an anatomically exact fit and in this way significantly facilitate orientation in the vascular system for the person carrying out the intervention. The vascular dataset is used because it is not desirable to be obliged to resort constantly to contrast agent during the intervention in order to make the vessels of the vascular system recognizable.
It is known for example to acquire an image dataset of the vascular system preoperatively, e.g., preinterventionally, for example as a two-dimensional or three-dimensional angiogram. In the two-dimensional or three-dimensional image dataset, at least some, (or, in some embodiments, all), of the vessels may be located automatically, thereby producing the vascular dataset. Segmentation techniques may be used, for example. The information relating to the course and the boundary of the vessels is then used to superimpose the anatomical information on the X-ray image. In this case, the course of the vessels may be described by a centerline, wherein the boundaries of the vessel may be indicated in addition, for example, also relative to the centerline. A well-known example that is representative of the modeling of vessels in a vascular system uses so-called “meshes,” in which the boundary of the vessels is considered as composed of in particular triangular mesh elements. The mesh elements may be assigned to a point on the medial line of the vessel, the line often being referred to as the “centerline”, which provides that for a known point on the centerline the mesh elements or rather their location may be determined by a well-known transformation rule. However, modelings of vascular systems are also known in which the boundary is described by a function, which may then also be stored relative to the centerline, in particular therefore parameterized by the position on the centerline.
An example of an interventional procedure in the vascular system of a patient is the repair of abdominal aortic aneurysms. An abdominal aortic aneurysm (AAA) is a vessel dilatation in the abdominal aorta. This is treated by insertion of a vascular prosthesis called a “stent graft.” For this purpose, guidewires and catheters may be introduced as instruments into the aorta by way of the patient's groin, by way of which the stent grafts may be inserted, in which case it is also conceivable to assemble the final stent from part-stents, (e.g., when the stent graft is to include the leg arteries as well). An example of this is the use of an aortic stent onto which a stent for the leg artery is “flanged” through a so-called “fenestration.”
The positioning of the vascular prostheses or stents is performed with extreme precision in order to avoid branch vessels becoming inadvertently occluded and suchlike.
A problem with such overlaid representations, which are based on information about the vascular system that is stored in a vascular dataset after having been obtained at an earlier time, is that the process of introducing the instrument itself may alter the vascular anatomy in comparison with the earlier time. If, for example, extremely stiff instruments are introduced, the anatomy, specifically the vessel through which the instrument is currently being guided, becomes deformed. If this deformation is not corrected in the overlay image, the consequence is an inaccuracy and a misregistration during the overlay, with the result for example that an instrument may appear at least partly outside a vessel. This may lead to uncertainties during the intervention, in particular when the overlay serves as an aid to navigation in the vascular system. It may also be noted at this juncture that the overlay image does not necessarily have to be an abstract image, but may include image data of the image dataset on which the vascular dataset is based. Frequently, however, it is mainly the boundaries of the vessels of the vascular system that are depicted. It may furthermore be pointed out also that a registration between the vascular dataset and the X-ray image is provided to achieve the anatomically correct overlay. This may be given by a registration that is present, for example, when the image dataset on which the vascular dataset is based was acquired by the same image acquisition device or X-ray device. It is also possible in this case to perform a conventional 2D-2D registration, a 3D-2D registration between the X-ray image, or an X-ray image recorded using the same acquisition geometry and the image dataset in the case of a patient remaining motionless.
DE 10 2010 012 621 A1 discloses a method and a device for automatically adapting a reference image. What is proposed therein is an adaption of a reference image that automatically corrects displacements, which may be brought about as a result of instruments being introduced, e.g., when a stent is inserted in an aorta. Toward that end it is aimed to distort the reference image in such a way that a current vessel course and a vessel course assumed from the position of the instrument are congruent once more, wherein it is intended that a smooth vessel course is to be preserved and various boundary conditions are to be taken into account, though without an actual procedure being disclosed. It was proposed to use the central line of an instrument located outside of a vessel as a new centerline of the vessel. However, this makes no allowance whatsoever for the specific actual circumstances.